Aluminum base bearing



ALUMINUM BASE BEARING No Drawing. Application October 6, 1951, SerialNo. 250,192

5 Claims. (Cl. 75147) This invention relates to an aluminum base alloyand particularly to an improved alloy of this type having propertiesrendering it especially suitable for use as a bearing material.

Many aluminum base bearing alloys, such as thetype disclosed in PatentNo. 2,238,399, which issued Apr l 15, 1941, in the name of Alfred W.Schluchter, are satisfactory bearing materials in most respects.However, such alloys cannot be satisfactorily heat treated so as toprovide sufficient hardness for many purposes. Accordlng ly, a principalobject of my invention is to provide an aluminum base bearing alloywhich can be heat treated so that it possesses a hardness comparable tothat of any conventional hardenable aluminum alloy and which, at thesame time, can be rolled into strip form by convennonal commercialmethods.

A further object of this invention is to provide such a heat treatablealuminum alloy which has exceptionally good score resistance when usedas a bearing. Aluminum and most of its alloys are generally quiteunsuitable for use in bearings for machine parts of iron for theadditional reason that aluminum tends to adhere to, or combine with, theferrous metal, thereby causing scoring or seizing. I have found,however, that by a suitable combination of alloying constituents thisdifiiculty can be overcome and an alloy produced having not onlyexcellent anti-friction properties but other characteristics especiallydesirable in a bearing material.

In accordance With my invention, therefore, the foregoing and otherobjects and advantages are attained to a particularly high degree in analuminum base alloy containing nickel, magnesium, cadmium and silicon.Inasmuch as the alloy thus produced is a much stronger metal than thealuminum alloys heretofore used for hearing purposes, solid bearings maybe made from it, no backing of steel or similar metals being necessaryfor many applications. Of course, this alloy also can be readily bondedto steel and many other metals and can be used on a backing.

Furthermore, the above-described alloy is characterized by much greaterhardness than related aluminum base alloys heretofore used, heattreatment of this alloy resulting in increasing its hardness as much asseveral hundred percent. Such a high degree of hardness is desirablebecause recently developed high compression engines impose exceptionallyheavy loads on bearings, thus creating an increased need in recent yearsfor greater hardness in such bearings. Similarly, the greater hardnessof my alloy permits it to be formed into a bearing having acorrespondingly longer fatigue life. As a result of this hardness, solidbearings made from this alloy also retain their original shapes muchbetter than many of the bearings which heretofore have been made ofsofter alloys. The former do not take a set at temperatures to whichthey are normally subjected, and they undergo a negligible amount ofshrinkage when removed from engines after extensive use. Despite theseaforementioned properties,

States Patent 0 the alloy can be easily rolled down by conventionalmethods.

In accordance with my invention, highly satisfactory bearing propertiesare obtained with an alloy having the following composition by weight:0.05% to 3.0% magnesium, 0.05% to 5.0% cadmium, 0.3% to 11.0% silicon,0.1% to 4.0% nickel and the balance substantially all aluminum. Variousincidental impurities may be included in this alloy in the usual smallamounts Without any substantial detrimental effects. For example, iron,which together with silicon is present in commercial aluminum, may bepresent in amounts up to 0.5% without causing any harmful results. Undersevere test conditions, alloys having the above composition showexcellent anti-friction properties so that bearings formed of this alloynot only do not score or gall when in contact with a rotating steelshaft, but neither the shaft nor the bearings show an appreciable amountof Wear after long and severe use. Similarly, resistance to cracking orcrumbling is also extraordinary.

The magnesium is added to increase the hardness of the bearing alloy, amagnesium content of only 0.05% being sufficient to provide a sufiicientdegree of hardness for many applications. inasmuch as the moltenmagnesium tends to oxidize during the alloying procedure, however, forbest results it is preferable that the mag nesium be added in amount-sequal to at least 0.2% of the weight of the alloy. Magnesium has anadverse effect on score resistance and friction properties, however, andas a result the magnesium content should not be higher thanapproximately 3.0%.

With additions of magnesium in amounts greater than approximately 0.5%,the increase in hardness is relatively slight. Moreover, if themagnesium content is not higher than this amount, the addition of nickeltends to offset the adverse effect of magnesium on the score propertiesof the alloy. Accordingly, a magnesium content ranging from 0.2% to 0.5%is preferred, approximately 0.5% magnesium generally being the optimumamount to be added.

The addition of cadmium greatly improves the score resistance of thealloy. Despite the fact that it has been generally recognized that theaddition of cadmium to aluminum causes slight loss of strength, I havefound that cadmium, in the presence of silicon, may be beneficiallyintroduced in amounts as large as 5.0% Without causing loss of strength.In fact, the resultant alloy is remarkably resistant to disintegrationunder impact or pounding such as occurs in severe bearing service.Moreover, the presence of cadmium does not effect the hardness if thealloy is subsequently heat treated. Although the affect of cadmium onboth strength and hardness is negligible in any event if added inquantities no greater than 5.0%, cadmium is a relatively soft metal andhence the cadmium content should not be higher than this amount.

I have also found that a cadmium content greater than 5.0% tends tocause this element to segregate out and settle to the bottom of thecasting during the solidification thereof in the form of the apparentlynearly pure metal. Thus, a too high cadmium content raises the cost ofthe alloy by increasing personnel expenses because of increased handlingcosts and the necessity of more detailed and careful supervision.Moreover, inasmuch as cadmium is also a relatively expensive andsomewhat rare metal, it is desirable to add only as much of this metalas is necessary to produce the desired results.

There is a marked improvement in score properties if cadmium is added inquantities up to 2.5%, but increasing the cadmium content beyond thisamount does not appreciably increase the score resistance of the alloy.Hence, cadmium preferably should be present in an oneness amount rangingfrom approximately 0.2% to 2.5% in order to providethe most desirableanti-friction proprties. Inasmuch as cadmium also tends to volatilize atthe temperature of molten aluminum, however, it often may be desirableto add slightly greater amounts of cadmium to offset this tendency forvolatilization. A cadmium content of at least 0.05% is necessary in allinstances to provide adequate score resistance.

The inclusion of silicon in my aluminum base bearing alloy also enhancesits score resistance. This property of silicon, plus the manner in whichit influences the effects of the cadmium present in the alloy and thefact that solidification shrinkage is lower as the silicon content israised, dictates thatthe alloy contain at least 0.3% silicon. Inasmuchas a high silicon content interferes with rolling processes, however,the maximum amount of silicon to be added necessarily is governed by themethod in which the article, such as a bearing, is formed. Accordingly,silicon should not be present in amounts greater than 5.0% in thewrought alloy because such an alloy needs to be rolled, while it may beadded in amounts as high as 11.0% in the cast alloy. While an increasedsilicon content improves score resistance, the addition of silicon inamounts greater than 5.0% provides only slight additional beneficialproperties in this respect. Accordingly, best results are obtained formost purposes when the silicon content is kept within a preferred rangeof 2.0% to 5.0%.

The inclusion of nickel, in combination with the magnesium addition,confers greater hardness on the aluminum base alloy. Moreover, nickel isalso particularly beneficial in that it improves the score properties ofthe alloy by tending to counteract the detrimental effects of magnesiumon score resistance. These desirable qualities with respect to hardnessand score resistance are provided by adding nickel in amounts rangingfrom approximately 0.1% to 4.0%.

While the hardness of the alloy will be substantially reduced if thenickel content is too low, the addition of nickel' in amounts greaterthan 4.0% does not appreciably increase the hardness but, on the otherhand, reduces the ductility of the resultant alloy, a high ductilitybeing necessary in wrought alloys. At the same time, the scoreresistance of the alloy is improved only slightly if the nickel contentis beyond 4.0%. Furthermore, it is generally not feasible to add morethan 4.0% nickel because increasing the nickel content above this amountraises the alloy costs by greatly increasing the difficulty in castingand fabrication of the cast parts. Also too high a temperature isrequired to place and hold greater amounts of nickel in solution in theliquid state. inasmuch as cadmium volatilizes excessively aboveapproximately 1400" R, a 4.0% nickel content is therefore about theupper limit that can be used with conventional foundry equipment, thisbeing the saturation point of the nickel in the aluminum alloy at thistemperature. Below this amount, however, nickel does not segregate out.

As a result of the above considerations, I have found that a nickelcontent within a preferred range of 0.3% to 1.5% provides excellentresults in all respects.

In the alloy hereinbefore described, it is necessary that both magnesiumand. nickel be used in conjunction to obtain the desired hardness. Theuse of either one of these metals alone in a quantity equal to thecombined amounts of the two metals will not provide the same degree ofhardness as the use of the two metals in combination.

The above alloy possesses the aforementioned desirable characteristicsto an outstanding degree when it consists of the following preferredcomposition: 0.5% magnesium, 2.0% cadmium, 4.0% silicon, 0.5% nickel andthe balance substantially all aluminum. As hereinbefore stated, otherincidental impurities may be presentin the above alloy, but for bestresults the amounts of these other ele ments' should be confined torelatively low proportions.

Accordingly, it is desirable that iron, for example, be present inamounts not greater than 0.5%.

In order to obtain the high degree of resistance to pounding, such as isencountered in a bearing, 1t is preferable that the alloy have aphysical structure typified by the absence of continuous networks ofmetallic elements. Convtntional alloying procedures may be employed withintermediate alloys, such as aluminum-silicon and aluminum'nickelalloys, being used to introduce the silicon and nickel. It is desirablethat the more volatile elements, such as the magnesium and cadmium, bethe last to be added to the melt in order to prevent their vaporization.in general, it is advisable to use the lowest temperature possible tokeep the cadmium from vaporizing. For example, I have found that thealuminum, silicon and nickel may advantageously be fused at atemperature in the order of approximately 1200" F., the melt thenpreferably being removed from the furnace. The magnesium and cadmium maynext be successively added to the melt, which is subsequently stirredand cast, usually in metal or graphite molds. The highest tem peraturesuitable for casting is that point at which the cadmium just begins tovaporize or smoke and, in order to avoid loss of metal, it is desirablenot to raise the temperature of the melt above this point. Accordingly,care should be taken not to permit the temperature to exceedapproximately 1400 F. The alloy may be either cast in the desired formfor use in bearings or it may be cast into ingots, rolled down to stripmaterial of the desired thickness, and bearing liners or other bearingelements formed from the stock.

Cast articles having a metallographic structure showing a continuousnetwork of segregated metal compounds may be improved as to strength andfatigue resistanceby suitable heat treatment. For example, I have foundthat a solution treatment at a temperature between approximately 900 F.and 950 F. for a period of twelve to fifteen hours is particularlyeflective to more completely dissolve the constituent elements and forma solid solution. Upon removal from the furnace following the solutointreatment, it is preferable to immediately cool the alloy by quenchingit in water. This treatment provides the alloy with a high degree ofductility, such as is desirable for rolling operations; and it may thenbe easily rolled down to strip material of the desired thickness.

A precipitation treatment may thereafter be employed to substantially.increase the hardness of the alloy. This process is preferably carriedout by heating the article for five to ten hours at atemperature in therange between approximately 350 F. and 400 F., a precipitation treatmentat 370 F. for eight hours being particularly satis factory. The alloythen may be again cooled, preferably in water, and suitably machined.Such a heat treating process results in an article which is three orfour times as hard as it was in the as-cast condition and whose fatiguestrength is proportionally improved.

The specific gravity of the above-described alloy is about one-thirdthat of a tin-bronze bearing alloy, and

the former has much greater resistance to fatigue or to cracking underthe pounding action to which bearings, such as connecting rod' bearings,are subjected. This property renders such an alloy particularly suitableas a bearing for use under extreme conditions, tests on such bearingsindicating the remarkable absence of wear, either of the bearing or theshaft. In addition, the alloy appears to be resistant to corrosion byacid constituents of lubricating oils which attack many other bearingcompositions.

It is to be understood that, while the invention has been described inconjunction with certain specific examples, the scope of the inventionis not to be limited thereby except as defined in the appended claims.

I claim:

1. A bearing formed of a hardenable alloy characterized by high scoreresistance consisting essentially 'of excess of 0.5% and the balancealuminum plus incidental impurities.

2. A bearing formed of an alloy consisting essentially of from 0.05% to3% magnesium, 0.05% to 5% cadmium, 0.3% to 11% silicon, 0.1% to 4%nickel, to 0.5 iron and the balance aluminum.

3. A bearing characterized by high anti-friction properties andresistance to disintegration under impact and to attack by acidsdeveloped in lubricating oils, said bearing being formed of an alloyconsisting of 0.05 to 3% magnesium, 0.05% to cadmium, 0.3% to 11%silicon, 0.1% to 4% nickel, and the balance aluminum plus incidentalimpurities.

4. A hearing formed of an alloy capable of being rolled into sheet formfrom cast ingots and having high anti-friction properties and fatigueresistance, said alloy consisting of 0.2% to 0.5% magnesium, 0.2% to2.5% cadmium, 2% to 5% silicon, 0.3% to 1.5% nickel and the balancealuminum.

5. A heat-treated and Worked, corrosion resistant hearing consistingessentially of from 0.05% to 3% magnesium, 0.05% to 5% cadmium, 0.3% to5% silicon, 0.1% to 1.5% nickel, iron not in excess of 0.5%, and thebalance aluminum.

References Cited in the file of this patent UNITED STATES PATENTSPritchard Apr. 19, Bossha rd Feb. 28, Sterner-Rainer Jan. 30, Pacz Sept.25, Kempf et a1 Jan. 8, Schlucter Apr. 15, Kempf et al. June 16, BagleyNov. 2, Hensel et a1. Apr. 15,

FOREIGN PATENTS Great Britain Feb. 22, Switzerland Feb. 29, GreatBritain June 2,

OTHER REFERENCES May 4, 1943.

1. A BEARING FORMED OF A HARDENABLE ALLOY ALLOY CHARACTERIZED BY HIGHSCORE RESISTANCE CONSISTING ESSENTIALLY OF FROM 0.2% TO 0.5% MAGNESIUM,0.2% TO 2.5% CADMIUM, 2% TO 5% SILICON, 0.3% TO 1.5% NICKEL, IRON NOT INEXCESS OF 0.5% AND THE BALANCE ALUMINUM PLUS INCIDENTAL IMPURITIES.